Aqueous Fire-Fighting Foam (AFFF) formulations contain water-soluble fluorosurfactants along with hydrocarbon surfactants. They are effective in extinguishing non-polar solvent fires. When an AFFF formulation comes in contact with a burning hydrocarbon fuel, the water, which contains both fluoro- and hydrocarbon surfactants, drains from the foam and forms a thin film on top of the burning fuel. This film does not sink, but due to its low surface energy (&lt;18 dynes/cm, which is lower than that of heptane), it spontaneously spreads across the surface of the burning fuel. There it acts as a vapor suppressant and, in combination with the aqueous foam, extinguishes the fire and prevents reignition of the fuel. It is important in this application that the foam have a long foam life on the hot fuel; otherwise the fuel can reignite, an event called burnback. A long foam life which provides burnback resistance is achieved by having a foam which is "wet", that is hydrated, and from which water can drain down onto the surface and replenish the seal. On a non-polar fuel like gasoline, this task is simple, since water and the water-soluble surfactants are not soluble in the fuel.
This task is considerably more difficult on polar fuels like isopropanol and acetone. Besides the fluoro- and hydrocarbon surfactants found in regular AFFF formulation, an Alcohol-Resistant (=AR) AFFF formulation contains a fluorochemical water-soluble but polar-solvent insoluble--also referred to as "alcoholophobic"--foam stabilizer (as described in this invention) along with a polysaccharide such as xanthan gum. When these additives come in contact with a burning polar fuel fire, they precipitate and give rise to a membrane which protects the foam from dissolving in the polar solvent. This membrane creates a vapor barrier which extinguishes the fire and prevents reignition of the fuel along with keeping the foam hydrated. Polysaccharides and/or high molecular weight synthetic polymers may be used in AR-AFFF formulations without a fluorochemical foam stabilizer and provide the same efficacy. The problem with a foam concentrate containing only polysaccharides and/or high molecular weight synthetic polymers is that its viscosity is high and the concentrate behaves in a thixotropic manner. It is difficult to use a high viscosity foam concentrate since it is hard if not impossible to pump through a fire nozzle. AR-AFFF formulations containing fluorochemical foam stabilizers require much lower amounts of polysaccharides and/or high molecular weight synthetic polymers, thus lowering the viscosity of the foam concentrate. Additionally, foam concentrates containing fluorochemical foam stabilizers in AR-AFFF formulations tend to behave in a Newtonian manner.
Fire fighting foam stabilizers containing at least one perfluoroalkyl group and water solubilizing functionalities such as carboxy and amido groups are described in U.S. Pat. Nos. 4,460,480 and in 5,218,021. French patent application 2637506-A describes an alcoholophobic and oleophobic fire extinguishing foam concentrate containing a polyhydroxy-polyamine containing at least one quaternary N atom and/or a polysaccharide which are chemically bonded to highly fluorinated C.sub.4 -C.sub.20 alkyl groups, instead of containing the fluorosurfactant separately and the polysaccharide or other alcoholophobic agent in the concentrated mixture.
Alcoholophobic fire fighting foam stabilizers containing at least one perfluoroalkyl group along with poly-quaternary amino and carboxy functionalities are described in world patents applications WO 9002110 A1 and WO 9003966 A1 along with publications by S. Szonyi in Fire Safety Journal, 16, pp. 353-365 (1990) and Progress in Colloid & Polymer Science, 81, 136-139 (1990).
Since quaternary amino groups cause incompatibility with the anionic surfactants used in fire fighting formulations, further improvements have been described in WO 94/18245. This reference teaches compounds which contain a combination of at least two perfluoroalkyl groups, amino groups other than quaternary amino groups, carboxylic groups and other water-solubilizing groups attached to amino groups. For example, U.S. Pat. No. 4,606,973 discloses aminoethylmethacrylate-acrylic acid copolymers in which the amino groups have been reacted with perfluoroalkyl carboxylic acids.
S. Szonyi, Com. Journ. Corn. Esp. Deterg., 22, pp. 297-304 (1991) describes a commercial state-of-the-art alcoholophobic foam stabilizer as a perfluoroalkylated polyamino acid.
An especially practical way to combine amino groups essential to foam stabilization with perfluoroalkyl-substituted compounds is to use readily available polyethyleneimine. The usefulness of polyethyleneimines in foam stabilizer formulations for polar solvent fires has been known for some time. For example, Japanese patent application S59-230566 describes useful foam stabilizers for polar solvents containing an anionic or amphoteric fluorosurfactant, polyethyleneimine of MW 4,000-100,000, and a polybasic acid compound.
U.S. Pat. No. 3,769,307 claims perfluoroalkylsubstituted polyethyleneimine compositions and the preparation thereof. This patent goes further to claim the use of such compounds as new textile finishes providing oleophobic properties. German Offenlegungsschrift 2 018 461 describes surface-active agents and foam stabilizers for polyurethane foams which are polyethyleneimines substituted by one or more perfluoroalkyl groups, as well as perfluoroalkyl-substituted polyamines containing up to 16 carboxy or sulfonic acid groups and/or hydrophilic amide groups. Although not directed toward foam stabilizer compounds for polar solvent fire fighting foams, the composition of this patent is described as very soluble in alcohol/water mixtures, but poorly soluble in alcohol (="alcoholophobic") and water itself, making it a candidate for such foam stabilizers. Indeed, the above cited WO 94/18245 reference describes the synthesis of a perfluoroalkyl- and carboxy-substituted polyethyleneimine from tetraethylene-pentamine, a perfluoroalkyl acyl chloride and chloroacetic acid.
Japanese laid open patent application 59-164073 discloses reaction products of polyethyleneimine and anionic fluorinated surfactants, providing the acidic and fluorinated component for effective foam stabilizers on polar solvents.
World patent application WO 96/05889 A1 also describes foam stabilizers consisting of polyamines having perfluoroalkyl groups attached to the polyamine through ester linkages, and containing additional hydrophilic groups and optionally a non-perfluoroalkyl hydrophobic group.
Effective foam stabilizers on polar solvents have to be essentially insoluble in these solvents. They most commonly are poly-perfluoroalkyl-substituted polyamino acid compounds, such as those described above. The present invention discloses compounds useful as foam stabilizers for fire-fighting foams used on polar-solvent fires which are polyethyleneimine derivatives containing anionic and nonionic water-solubilizing groups, and further substituted with a mixture of perfluoroalkyl-allyloxy and perfluoroalkyl-iodopropyloxy groups or poly-perfluoroalkyl-fluoroallyl groups.
Mono-perfluoroalkyl (=R.sub.F) substituted amino acids have long been known to be excellent amphoteric surfactants, reducing the surface tension of water to as low as 16 dynes/cm. Such compounds, obtained by the reaction of an R.sub.F -ethylthiol, maleic anhydride and a di- tri- or tetra amine and containing up to two R.sub.F, carboxy- and amino groups are described for instance in U.S. Pat. Nos. 4,069,244 and 4,161,602. Di- and poly-R.sub.F -polyamino acids obtained by reaction of a di-R.sub.F -diol with a dianhydride and a diamine and containing 2-6 R.sub.F -groups, 4-10 carboxy and two tertiary amino groups are described in U.S. Pat. No. 4,153,590. These amphoteric compounds have been found useful as surface-active agents and film formers in aqueous and resin formulations.
Another class of amphoteric compounds with similar properties and also containing R.sub.F -, acid and amino groups, and which are useful to impart oil repellency to paper products are di-R.sub.F -amino acids obtained by reaction of an amino acid, allyl glycidyl ether and R.sub.F -iodide as described in U.S. Pat. No. 5,491,261. This synthetic route, using an R.sub.F -iodide rather than an R.sub.F -thiol as the starting material, is more cost-effective, since it can be carried out in higher yields and produces much less waste.
It has now been discovered that by a similar route polymeric R.sub.F -amines, including polymeric R.sub.F -amino acids of the type which are useful as foam stabilizers for polar solvent fire-fighting foams, and which contain a plurality of R.sub.F groups as well as amino, and carboxy or other hydrophilic groups, can conveniently be prepared in similarly high yields and essentially without waste from a polymer containing a plurality of primary and/or secondary amino groups and a plurality of acid groups, by reaction with allyl glycidyl ether (=AGE) followed by addition of R.sub.F -iodide and partial dehydrohalogenation. The resulting mixture of poly-perfluoroalkyl-allyloxy--and poly-perfluoroalkyl-iodopropyl-substituted-polyamino acids are useful as grease-proofing agents for paper, but more importantly, they have been found to act as excellent foam stabilizers for Aqueous Fire-Fighting Foam (AFFF) formulations used on polar solvent fires.
Similar compounds, which are poly-perfluoroalkyl-fluoroallyl-substituted-polyamino acids and which are excellent foam stabilizers for AR-AFFF agents can be prepared by reaction of polyethyleneimines with a perfluoroalkylethyl iodide, followed by reaction with amino-reactive acid compounds such as chloroacetic acid or succinic anhydride. This reaction is believed to proceed through a perfluoroalkylethylene intermediate and subsequent elimination of HF, resulting in a 3-perfluoroalkyl-2-fluoro-allylamine structure. The addition reaction of perfluoroalkylethylenes to primary and secondary amines is described in U.S. Pat. Nos. 3,535,381 and 4,853,141.
It has also been found that the acid functionality is not essential to the performance of the compounds, but can be replaced by other hydrophilic groups, such as amide and/or hydroxy groups. Nonionically-substituted poly-R.sub.F -polyethyleneimines were furthermore found to give superior performance with saltwater; likewise, phosphoric acid-substituted poly-R.sub.F -polyethylene-imines were found to give superior performance with saltwater. Performance when mixed with saltwater is a major concern in firefighting operations aboard ships and in harbors.
The use of nonionically-substituted and phosphoric acid substituted poly-R.sub.F -polyethyleneimines as foam stabilizers in salt water fire-fighting foam formulations is thus another object of this invention.